hwmon: (npcm750-pwm-fan) Fix crash observed when instantiating nuvoton,npcm750-pwm-fan

hwmon: (npcm750-pwm-fan) Fix crash observed when instantiating nuvoton,npcm750-pwm-fan

Commit 89fec128d5d1 ("hwmon: (npcm750-pwm-fan) Add NPCM8xx support")
introduced support for PWM fans on Nuvoton's npcm845 SoC. This chip
supports three PWM modules with four PWM channels each. The older npcm750
only supported two PWM modules. The commit did not take into account that
the older SoC only supported two PWM modules. This results in a crash if
npcm750 is instantiated when the code attempts to instantiate the
non-existing third PWM module.

Unable to handle kernel paging request at virtual address e0aa2000 when write
[e0aa2000] *pgd=04ab6811, *pte=00000000, *ppte=00000000
Internal error: Oops: 807 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Tainted: G                 N 6.7.0-next-20240112-dirty #3
Hardware name: NPCM7XX Chip family
PC is at npcm7xx_pwm_fan_probe+0x204/0x890
LR is at arm_heavy_mb+0x1c/0x38

Fix the problem by detecting the number of supported PWM modules in the
probe function and only instantiating the supported modules.

Fixes: 89fec128d5d1 ("hwmon: (npcm750-pwm-fan) Add NPCM8xx support")
Cc: Tomer Maimon <tmaimon77@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>